 If the controller designated in the I/O address is busy or disabled, the dynamic path selection allows an alternate
path to the device to be established via another storage
director and the other controller in the model AA.Prior to the 1981 introduction of the 3880 director, CKD records were synchronously accessed, all activities required that one CCW be ended and the next initiated in the gaps between the CKD fields.The gap size placed limitations on cable length but did provide for very high performance since complex chains of CCWs could be performed by the subsystem in real time without use of CPU memory or cycles.